SPEED & ASR SENSORS - E-300 TD. ?

[HERBIEMERCMAN]

Hi Everyone, This a question for "the dying breed" the old Merc stuff.
I have a 1997 e-300 td estate and recently the BAS light comes on at random for no apparent reason.
From memory there is a reluctance ring on each hub and this has a sensor creating a "dopler" signal, this signal moniters the rotational harmony of all four wheels and if any wheel goes outside of 7% on the rotational harmony, then the warning light comes on or limp home occurs from the ASR.

My question is if this is caused by a faulty sensor how do you locate it?
I also have a faint memory of Malcolm telling me that the main speed sensor is located on the front near side wheel?, i think this also feeds the cruise control?

Hope there is someone still out there can can advise. Many thanks. Herbie.

 

[Frontstep]

Clean them, sensors hole and rings for starters youtube will show how, I found a broken reluctor ring and Mercedes do sell them separately.
Withdrawing the sensors might show them covered in crud.

 

[yorkshire1]

not sure about the 210 but as far as I know the earlier 202s only had one sensor for the rear wheels located in the rear diff,have you checked the brake light switch because if thats fauly it throws the abs/asr/ bas out

 

[om613]

There's not a 'non-STAR' test for the brake light switch other than ...does the cruise control still work? If
so, then it's not the brake light switch putting the lights on.

You can test the resistance of the 4 wheel speed sensors with a DVM, they're ~ 1.5K Ohms.
The rear reluctor rings can fall off the half shafts, as rust splits them. The fronts not so, they're are cast into the hubs.

 

[HERBIEMERCMAN]

Many thanks guys that is good information.
I changed the foot brake switch some weeks back and it solved the problem for a while, i think the speed sensors do need attention, i have owned the car from new, so 20 years and 240,000 miles and as far as i know the speed sensors and reluctance rings have not had any attention.The BAS and ASR warning lights come on at random and the cruise control works but keeps surging, also at speed on the M/ways the lights come on and the steering tightens up.
I will ask my "Inde" to look at the set up. Herbie.

 

[om613]

You've not put the spare wheel or another wheel on recently, have you?

 

[HERBIEMERCMAN]

Hi om613, I know why you ask this about the wheels as i have been "down this road" before, many years back i fitted 18 inch wheels and the "rolling ratio" on the front tyres were more than 7% less than the rears, i had to replace the front tyres to brink the ratio within the 7% max. I learned from this situation but forgot about the spare wheel being the original 16 inch, i had to drive from Stranraer in "limp home", max 45 mph.
I have considered the current tyres now being half worn, but they have all worn equally, so this is not my problem. Herbie.

 

[Doug1234]

BAS , is that not a valve in servo that opens to let extra vacuum in to help pull pedal down for better.braking effort.
Detects quick pedal movement and starts to operate, nothing to do with wheel sensors as abs /asr use them ?.

 

[HERBIEMERCMAN]

Hi Doug1234, Thank you for that info, i have just been to collect my car from my local "Inde" and he got a fault code pointing to the foot brake switch being at fault, this switch was changed in January this year and was an "after market" one from Euro Parts, he says he has replaced the switch with another "after market" one and if this fails then an "OEM" switch will be fitted. I guess it is always a gamble to use second hand parts or "after market" parts, but over the last 22 years i have used more of these than the "OEM" stuff. The cost of "OEM" stuff is very expensive, all be it for things like this brake switch and glow plugs, then obviously the "OEM" parts make most sense. Herbie.

 

[om613]

OEM BLS is £14, pattern about half that.

 

[HERBIEMERCMAN]

The replaced foot brake switch has not worked, at 70mph on m/way all lights came on ABS/ASR/BAS, and the steering tightened up/ is it another OEM switch, or the speed sensors and reluctance rings serviced ? Herbie.